Partial vacuum operation of arc discharge for controlled heating

ABSTRACT

An electrical discharge, suitable for heating optical fibers for processing, is made in a controlled partial vacuum, such that saturation of available ionizable gas molecules is reached. The workpiece temperature is thereby made to be a stably controlled function of the absolute air pressure and is insensitive to other conditions. A system and method accomplishing the foregoing are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119(e) from U.S.Provisional Patent Application 61/621,274 filed Apr. 6, 2012, entitledPARTIAL VACUUM OPERATION OF ARC DISCHARGE FOR CONTROLLED HEATING, thedisclosure of which is incorporated herein in its entirety by reference.

FIELD OF INTEREST

The present inventive concepts relate to the field of systems andmethods for optical fiber processing, and more particularly to the fieldof systems and methods using heat for optical fiber processing.

BACKGROUND

In the manufacture of devices using optical fibers, it is commonlyrequired to heat the fibers in a controlled manner so that they may bespliced, coupled, shaped, annealed, tapered, diffused, expanded, flamepolished, cleaned, or stripped of coatings. An electrical discharge iscommonly employed for this purpose. This electrical discharge is knownin the industry as an “arc.” However, according to some sources, adischarge of this current level is not a true arc, but a glow dischargethat generates a hot plasma.

The arc is normally formed between the sharply pointed tips of a pair ofelectrodes, typically made of tungsten and spaced 1 mm to 10 mm apart.Larger electrode spacing is required for splicing multiple fibers atonce (fiber ribbons), and for larger diameter fibers. The optical designof some splicers may also require the electrode spacing “gap” to belarger in order to prevent the electrodes from physically occluding theoptical path.

The voltage applied to the electrodes may be DC (typically inconjunction with smaller electrode spacing) or AC (which allows a largerspacing between the electrode tips—up to 10 mm or more). The voltagerequired to initiate the discharge is determined by Paschen's Law, whichrelates the breakdown voltage of a gap between electrodes to a (complexand non-linear) function of the gas present in the gap (typicallyordinary air), pressure, humidity, electrode shape, electrode material,and gap distance. Many of the parameters required to apply Paschen's Lawto this system are not known, so little quantitative theoreticalanalysis of splicer arcs has been done. Typically, the initiatingvoltage is determined experimentally to be in the range of 5 kV to 30kV.

FIG. 1 shows a schematic representation of a typical prior art fiberprocessing device using an electrical discharge as a heat source, knownas a “fusion splicer”. This device has as its primary purpose thesplicing of two fiber ends together, but may also be used for otheroperations, such as tapering. The two fiber ends are held by fixtures(3,4) which can be positioned in at least two axes each. An ArcDischarging Unit (5) provides controlled high voltage to two pointedtungsten alloy electrodes (1,2). A programmable control unit (6)positions the fibers and controls the operation of the Arc DischargingUnit. Typically, these mechanisms are used in conjunction with one ormore cameras and associated optics (not shown) to locate the fibers forpositioning and to analyze the resulting splice quality.

Once the arc has been initiated, sustained ionization of the plasma inthe discharge requires a lower voltage than initially applied. Theimpedance (ratio of applied voltage to current) of the plasma as acircuit element is difficult to predict. Splicer arcs are even suspectedto exhibit negative incremental impedance at some frequencies andcurrent levels. These characteristics make “constant voltage” operationof a splicer arc very difficult to achieve. Therefore, most such systemsare controlled to provide a constant average current. This correlates ina reasonably predictable way with the observed power delivered to thedischarge and the resulting temperature of the fibers.

However, the accuracy, precision, and repeatability of such controlmethods is subject to many uncontrolled factors. Air pressure, humidity,air temperature, electrode spacing, electrode cleanliness, and electrodegeometry produce unacceptably large changes in the temperature reachedat the working surface of the fibers. The electrodes oxidize away duringuse, which expands the gap between the electrodes, blunts their points,and contaminates their emitting surfaces.

As a result, various procedures have been developed to renormalize therelationship between the setpoint arc current and the resulting fibertemperature. These procedures normally consist of an “arc check” whereinthe arc discharge is operated at various power levels, and the resultingdistortion or incandescence of the fibers is observed by a camera toprovide information used to recalibrate the system for atmospheric andelectrode conditions. These procedures are unsatisfactory in manyrespects, as they consume time, electrode life, and optical fiber, whileproviding only a temporary and partial solution to the problem ofchanges in the fiber temperature.

SUMMARY

In accordance with one aspect of the present disclosure, provided is anoptical fiber processing system. The system comprises at least twoelectrodes; at least one fiber holder configured to hold an opticalfiber; an airtight enclosure providing a partial vacuum, within whichthe at least two electrodes are disposed such that a portion of theoptical fiber is maintained between the at least two electrodes withinthe airtight enclosure; and an arc discharging unit configured toselectively control a drive current supplied to the at least twoelectrodes to control a discharge region generated by and between the atleast two electrodes to heat the portion of the optical fiber.

In various embodiments, the at least two electrodes can be threeelectrodes.

In various embodiments, the at least two electrodes can be more thanthree electrodes.

In various embodiments, the system can further comprise a pressuresensor configured to sense a pressure within the airtight enclosure.

In various embodiments, the at least one fiber holder can be at leastone multi-axis positioner.

In various embodiments, the system can further comprise a vacuumgenerating venture configured to generate the partial vacuum within theairtight enclosure.

In accordance with another aspect of the invention, provided is a methodof processing an optical fiber. The method comprises providing at leasttwo electrodes, at least two fiber holders configured to hold an opticalfiber, an airtight enclosure providing a partial vacuum, within whichthe at least two electrodes are disposed such that a portion of theoptical fiber is maintained between the at least two electrodes withinthe airtight enclosure; and using an arc discharging unit, selectivelycontrolling a drive current supplied to the at least two electrodes tocontrol a discharge region generated by and between the at least twoelectrodes to heat the portion of the optical fiber.

In various embodiments, the at least two electrodes can be threeelectrodes.

In various embodiments, the at least two electrodes can be more thanthree electrodes.

In various embodiments, the method can further comprise sensing apressure within the airtight enclosure.

In various embodiments, the method can further comprise generating avacuum within the airtight enclosure.

In accordance with another aspect of the invention provided is aworkpiece processing system. The system comprises at least twoelectrodes; a workpiece holder configured to hold a workpiece; anairtight enclosure providing a partial vacuum, within which the at leasttwo electrodes are disposed such that a portion of the workpiece ismaintained between the at least two electrodes within the airtightenclosure; an arc discharging unit configured to selectively control adrive current supplied to the at least two electrodes to control adischarge region generated by and between the at least two electrodes toheat the portion of the workpiece; a pressure sensor configured to sensea pressure within the airtight enclosure; and a vacuum generatingventure configured to generate the partial vacuum within the airtightenclosure.

In various embodiments, the at least two electrodes can be threeelectrodes.

In various embodiments, the at least two electrodes can be more thanthree electrodes.

In various embodiments, the at least one workpiece holder can be atleast one multi-axis positioner.

In various embodiments, the workpiece can be at least one fiber.

In various embodiments, the at least one fiber can be a small diameterfiber.

In various embodiments, the at least one fiber can be a large diameterfiber.

In various embodiments, the at least one fiber can be more than onefiber.

In various embodiments, provide can be a device as described in thefigures.

In various embodiments, provide can be a system as described in thefigures.

In various embodiments, provide can be a method as described in thefigures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent in view of the attacheddrawings and accompanying detailed description. The embodiments depictedtherein are provided by way of example, not by way of limitation,wherein like reference numerals refer to the same or similar elements.The drawings are not necessarily to scale, emphasis instead being placedupon illustrating aspects of the invention. In the drawings:

FIG. 1 shows a schematic representation of a typical prior art opticalfiber processing device using an electrical discharge as a heat source,known as a “fusion splicer;”

FIG. 2 illustrates the effect of current and pressure on thedistribution of energy within the arc discharge region DR, between twoelectrodes, of an optical fiber processing device providing a partialvacuum, in accordance with aspects of the invention;

FIG. 3 illustrates, in schematic form, an embodiment of an optical fiberprocessing device providing a partial vacuum, in accordance with aspectsof the invention;

FIG. 4 shows another view of an embodiment of an optical fiberprocessing device providing a partial vacuum, in accordance with theinvention; and

FIG. 5 shows an expanded cross section of an embodiment of the flexibleseal mechanism.

DETAILED DESCRIPTION

Various exemplary embodiments will be described more fully hereinafterwith reference to the accompanying drawings, in which some exemplaryembodiments are shown. The present inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set forth herein.

It will be understood that, although the terms first, second, etc. arebe used herein to describe various elements, these elements should notbe limited by these terms. These terms are used to distinguish oneelement from another, but not to imply a required sequence of elements.For example, a first element can be termed a second element, and,similarly, a second element can be termed a first element, withoutdeparting from the scope of the present invention. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element is referred to as being “on”or “connected” or “coupled” to another element, it can be directly on orconnected or coupled to the other element or intervening elements can bepresent. In contrast, when an element is referred to as being “directlyon” or “directly connected” or “directly coupled” to another element,there are no intervening elements present. Other words used to describethe relationship between elements should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like may be used to describe an element and/or feature'srelationship to another element(s) and/or feature(s) as, for example,illustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use and/or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” and/or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.The device may be otherwise oriented (e.g., rotated 90 degrees or atother orientations) and the spatially relative descriptors used hereininterpreted accordingly.

In accordance with the inventive concept, provided are a system andmethod where an arc is formed between two or more electrodes in at leasta partial vacuum, where control of the vacuum provides a heating limitirrespective of other parameters that would otherwise affect the heatingtemperature.

A glow discharge (“arc”) comprises a flow of electric current throughionized air. The current is primarily transmitted by ions of nitrogenand oxygen, and to a much lesser extent, other atmospheric gasses. Asthe current provided to the discharge increases, an increased proportionof the air molecules along the path between the electrode tips becomeionized, increasing the energy density and the resulting fibertemperature. Eventually, the molecules available along the most directpath all become ionized, and the impedance of the discharge becomes verylow. Further increases in drive current cannot increase the energydensity directly in the gap between the electrodes, and so the volume ofthe discharge expands instead. However, this normally occurs only atenergy densities which produce temperatures much higher than is usefulfor processing most optical fibers. Therefore, all prior art arcdischarges for fiber processing are operated well below this saturationpoint.

FIG. 2 illustrates the effect of current and pressure on thedistribution of energy within the arc discharge region DR, between twoelectrodes 1, 2. FIG. 2A shows an arc discharge at moderate power atnormal atmospheric pressure. FIG. 2B shows the result of increasing thedrive current while maintaining the same pressure—the discharge regionDR is well below saturation, so the energy density increases with only asmall expansion of the size of the discharge region DR. In FIG. 2C, thedrive current is at the same increased level, but the pressure has beenreduced. Since at this pressure the discharge region DR is saturatedwith current, the energy density remains constant and the dischargeregion DR expands proportionally. The expansion is in the proportionthat the cross sectional area of the discharge, perpendicular to thecurrent flow, is linearly proportional to the drive current.

When the ambient atmospheric pressure in which the discharge occurs isreduced, fewer air molecules per volume are available to be ionized andserve as charge carriers. Therefore, the maximum energy density andresulting maximum temperature are lower and are reached at a lower levelof drive current. By controlling the air pressure in the arc region, anupper limit to the fiber temperature is established. The arc driveelectronics need only provide sufficient current to saturate theavailable ionizable air molecules at the chosen pressure. The fibertemperature becomes almost completely insensitive to the condition,spacing, and geometry of the electrodes 1,2, as well as to anydeficiencies in the accuracy of the current control of the arc driveelectronics. The discharge current (provided that it is greater than thesaturation current of the gap between the electrodes) controls only thevolume of the arc discharge, not its temperature. Most fiber processingoperations, such as splicing, are far more sensitive to temperature thanto the area of the heated surface, so this produces more stable resultsthan prior art methods. The arc current may still be varied as requiredto produce a larger or smaller discharge volume, as may suit therequirements of the application for which the arc is being used, e.g.,splicing, tapering, stripping, lensing, and so on.

In a test of a prototype device embodying the invention, the arcdischarge was adjusted to the full drive current capability of thedevice. At standard pressure this current results in temperatures andenergy densities sufficient to rapidly boil silica fiber to vapor(>2230° C.), even for large fibers of 1 mm diameter. The air pressurewas adjusted to approximately 0.1 atm. A 10 μm silica fiber was placedin the discharge. It was found that the resulting temperature (estimatedat 1200° C.) was just sufficient to allow the fiber to be inelasticallydeformed by an applied force over several seconds. Reduction of theapplied current by approximately 80% greatly reduced the area of thedischarge, but the deformation rate of the fiber within the dischargeregion was unchanged, in accordance with the theory underlying theinvention.

In a device embodying the invention, the temperature applied to thefibers is almost purely a function of the absolute pressure within theenclosure. This pressure can be sensed and controlled by well-knownmeans within very tight limits. This eliminates the need for “arc check”functions and provides a highly stable, repeatable temperature for theprocess. Furthermore, little or no change to the pressure level isrequired for fibers of differing diameters. Since the heat zoneionization potential is entirely saturated, the desired energy densityand temperature will remain substantially constant, with the addition ofa larger or smaller mass of fiber having little effect. Control of thepressure can be maintained with much greater precision, accuracy, andrepeatability than control of current and/or voltage of the complexwaveforms of a typical arc discharging unit.

To implement the invention, the working area of the arc discharge andfibers (or other workpiece) is enclosed in a structure that can beevacuated to the required reduced pressure while still allowing accessfor the fiber, fibers, or other workpiece, as well as any accompanyingpositioners, fixtures, cameras, optics, illumination, and so forth. Avariety of configurations are possible and will be apparent to oneskilled in the art.

In one configuration, an entire splicer or other device could bedisposed within the vacuum chamber. In another possible configuration,only the immediate volume surrounding the arc discharge may be enclosed,e.g., with bellows or other devices allowing positioners to move thefibers and windows provided for an optical system if required. In yetanother configuration, the positioners and optics may be enclosed, withthe electronic control mechanisms located outside the enclosure. A widevariety of devices to allow pressure-tight access for wires, opticalpaths, and mechanical mechanisms are known and may be used to enable anyof a variety of particular configurations. All of these possibleconfigurations embody the present invention and may be selectedaccording to other requirements of the use to which the invention may beput.

The enclosure for the arc discharge region, of whatever configuration,must have provisions for maintaining a stable absolute pressure at therequired level. The air may be evacuated by a pump or venturi device, asexamples. A pressure sensor would be provided to detect the pressurelevel and control the pump or air flow to the venture as required.

The absolute pressures of interest are typically in the range of 0.05atm to 0.9 atm (0.7-13.2 psi absolute/38-684 torr). This is well abovethe pressures at which X-ray production from the electrical dischargewould become a danger, or at which standard lubricants and materials formechanical motion cease to function well.

It will be seen that it is also possible to provide for replacing theremaining air within the enclosure with other gases. For example, aninert gas, such as argon, may be used. This would have the benefit ofdisplacing any humidity present in the air, as well as preventingoxidation of the tungsten electrodes. Other gases may also be used forvarious desired effects, while remaining within the scope of theinvention.

The number of electrodes generating the arc discharge is not limited totwo. Three or more electrodes, driven by appropriate multi-phase drivecircuits can be employed, as in the 3sae Technologies Inc. “Ring ofFire” technology. (See, e.g., U.S. Pat. No. 7,670,065, U.S. Pat. No.7,922,400, U.S. Pat. No. 7,985,029, and US Pat. Pub. 2011-0277511, eachof which is incorporated herein by reference in its entirety).

When the arc discharge is operated at the saturation point, it is nolonger necessary to provide sharply pointed electrodes. The electrodescan be made with flat or spherical ends. Alternatively, the electrodescan be made “T” shaped and have “arms” extended along axes parallel withthe axis of the fiber. The discharge region can thereby be shaped toprovide a heating zone that extends along the axis of the fiber forseveral millimeters. If three electrodes are used, the discharge forms a“tunnel” in the form of an open-ended triangular prism, heating thefiber evenly around its circumference and for a substantial length alongits axis. This provides substantial advantages in fiber tapering anddiffusion operations. It will be realized by one skilled in the art thata wide variety of interchangeable electrode configurations can beprovided to shape the heating zone according to differing operationalrequirements. All of these possibilities are enabled by the method ofarc discharge in partial vacuum and are embodiments of the presentinvention.

Several additional advantages are also obtained by operation of the arcin partial vacuum. By increasing the drive current beyond the saturationpoint, the discharge can be expanded to cover a much wider area of thefiber than is possible with prior art arc discharge devices or even withfilament heaters. This is advantageous in splicing many fibers, as wellas for tapering, dopant diffusion, annealing, and other operations.Since atmospheric pressure is directly controlled, it is no longer anuncontrolled variable affecting delivered temperature. Furthermore,sensitivity to humidity and air temperature is reduced to the point ofnegligibility. Also, air currents from convection within the enclosureare minimized and air currents from external drafts or wind areeliminated entirely.

Another advantage is that the decreased partial pressure of oxygengreatly reduces oxidation of the electrodes as they become heated. Thisincreases electrode life and reduces deposition of tungsten oxide on thefibers or other workpieces.

Yet another advantage is that the arc discharge becomes much easier toinitiate. At standard atmospheric pressure, special electronictechniques (known in the art) must be used to ensure that the relativelyhigh initiating voltage is reached to start the arc. This initial highvoltage requires heavy insulation of the output transformers and outputwiring of the arc discharge electronics. Paschen's Law states that theinitiating voltage is proportional to absolute air pressure asV≈P/ln(P). Therefore, reduced pressure (for pressures 0.01 atm<P<1 atm)requires a lower initiating voltage, with subsequently reducedrequirements for insulation. The requirements for a sharp, preciselyshaped point on the electrodes are also eased or eliminated at lowerpressures.

Still another advantage is that any gases or fumes produced by theheating operation are contained within the vacuum enclosure andexhausted by the vacuum pump or venture, if provided. They may bereadily vented or captured as required by safety and environmentalregulations and requirements.

Although the uses of the arc discharge in partial vacuum are describedherein as they apply to the processing of optical fibers, it will berecognized that the present invention has much broader applicability. Inmany cases wherein a glow discharge is used to as a heat source, thissame method or an equivalent will provide the same or similar benefits.

A variation of the process is to operate the arc discharge at elevatedpressure (above 1 atm absolute). This foregoes many of the advantages ofthe normal use of the invention, but does allow for higher energydensity and temperature to be reached if required. This increasedtemperature is suitable, for example, for performing splicing or otheroperations on sapphire (Al2O3) fibers and optical waveguides.

By operating the arc discharge at elevated pressure, but at currentlevels below the threshold of ion saturation, the arc discharge can bemade at lower temperatures, but within a very compact and narrow volume.This method can be used when it is desired to heat only a very smallregion of a fiber or other workpiece. An application of this modifiedprocess would be to heat small regions of a fiber at regularly spacedintervals along its axis in order to create an optical grating.

An apparatus suitable for implementation of the reduced pressure methodcan be readily adapted to be operated in an elevated pressure mode aswell.

FIG. 3 illustrates in schematic form a preferred embodiment of anoptical fiber processing device 100 providing a partial vacuum,according to aspects of the invention. An airtight enclosure 8 isprovided to house two multi-axis positioning mechanisms 3,4 and the arcdischarging electrodes 1,2. Cameras and optics, not shown, can also beprovided within the enclosure to observe the positioning of the fibers.The fiber 11 (which can be a single piece, or two pieces in the processof being spliced together) extends into the enclosure from outside. Thefiber 11 is at least one fiber, and could include more than one fiber orfiber ribbon. A flexible seal 10 prevents ingress of air around thefiber. A programmable control mechanism 6, which can be a computerand/or a dedicated microcontroller board, controls the operation of thedevice. A vacuum-generating venture 12 is coupled to the enclosure by atube to evacuate the air. An absolute pressure sensor 13 detects thepressure level within the enclosure.

The electrodes 1,2 can be constructed so that they may readily beinterchanged with electrodes of different shapes as desired. Inaddition, an arc discharging unit 5 has provisions for driving a thirdelectrode (not shown) which may be readily added for “Ring of Fire”(three-phase) operation, discussed above.

FIG. 4 shows another view of an embodiment of an optical fiberprocessing device providing a partial vacuum 100, in accordance with theinvention. The top surface of the enclosure can be closed by a movablelid 7 having a flexible seal 9, which mates with the flexible seal 10 inthe bottom portion of the enclosure 8, so as to seal around the fiber11. To load and remove the fibers, or to make adjustments to theinterior mechanisms, the lid 7 can be readily lifted to an upperposition. When the lid is lowered and the enclosure is evacuated, airpressure forces the lid tightly against the lower portion of theenclosure 8, deforming the seals (e.g., O-rings) 9,10 so as to sealtightly around the fiber.

FIG. 5 shows an expanded cross section of an embodiment of the flexibleseal mechanism. The flexible seals 9,10 are o-rings in this embodimentcontained within grooves machined into the aluminum enclosure 8 andenclosure lid 7.

The various positioning mechanisms, optics, and electronics of thepreferred embodiment are not dissimilar to others well known in the art.The present invention is embodied in the airtight enclosure andprovisions for maintaining a controlled partial vacuum in the area wherethe arc discharge occurs. The operator, an engineer providing programmedprocesses for the operator, or an automated feature realized by thecontrol unit 6 selects according to empirically determined data anabsolute pressure corresponding to the desired temperature to be appliedto the fibers or other workpiece. The arc discharging unit 5 need onlybe controlled so as to provide a current sufficient to saturate theionization of the arc discharge region for the installed electrodeconfiguration. If desired, the current can be further increased toexpand the heating zone. Because of the benefits of the presentinvention, the temperature applied to the workpiece can be expected toremain constant over time, electrode condition changes, and on otherunits of the machine embodying the invention.

While the foregoing has described what are considered to be the bestmode and/or other preferred embodiments, it is understood that variousmodifications can be made therein and that the invention or inventionsmay be implemented in various forms and embodiments, and that they maybe applied in numerous applications, only some of which have beendescribed herein. It is intended by the following claims to claim thatwhich is literally described and all equivalents thereto, including allmodifications and variations that fall within the scope of each claim.

1.-20. (canceled)
 21. A method, comprising: establishing an arcdischarge in a gap between at least two electrodes within a gas-filledchamber, thereby producing a heat zone in the gap; and controlling anupper temperature limit within the heat zone by controlling a gaspressure within the chamber.
 22. The method of claim 21, furthercomprising: ionizing the gas within the heat zone so that the arcdischarge reaches saturation for a chosen gas pressure.
 23. The methodof claim 22, wherein ionizing the gas within the heat zone comprises:bringing a current level of the arc discharge to at least a saturationlevel.
 24. The method of claim 22, further comprising: controlling avolume of the heat zone by selectively controlling a drive currentsupplied to one or more of at least two electrodes.
 25. The method ofclaim 24, wherein an energy density of the arc discharge remainssubstantially the same at different volumes of the heat zone.
 26. Themethod of claim 21, further comprising: generating at least a partialvacuum within the gas-filled chamber.
 27. The method of claim 21,wherein the at least two electrodes is at least three electrodes. 28.The method of claim 21, further comprising: positioning at least oneoptical fiber within the heat zone for processing.
 29. The method ofclaim 28, wherein the processing comprises: splicing at least twooptical fibers the heat zone.
 30. The method of claim 28, wherein theprocessing comprises at least one of: tapering the at least one opticalfiber the heat zone; annealing the at least one optical fiber in theheat zone; stripping the at least one optical fiber in the heat zone; orlensing the at least one optical fiber in the heat zone.
 31. The methodof claim 21, wherein the chamber is an airtight chamber.
 32. Anapparatus, comprising: a chamber configured to maintain a gas; aplurality of electrodes within the chamber and arranged to generate anarc discharge in a gap between the at least two electrodes to establisha heat zone in the gap; a controller configured to control a gaspressure within the chamber to responsively control an upper temperaturelimit within the heat zone.
 33. The apparatus of claim 32, furthercomprising: an arc discharge unit configured to supply a drive currentto the at least two electrodes at a level sufficient to ionize the arcdischarge to saturation for a chosen gas pressure.
 34. The apparatus ofclaim 33, wherein the arc discharge unit is further configured toselectively control the drive current supplied to one or more of atleast two electrodes, above saturation, to control a volume of the heatzone, wherein an energy density of the arc discharge remainssubstantially the same at different volumes of the heat zone.
 35. Theapparatus of claim 32, further comprising: a venturi that generates apartial vacuum within the chamber.
 36. The apparatus of claim 32,wherein the at least two electrodes is at least three electrodes. 37.The apparatus of claim 32, further comprising: a positioner systemconfigured to position at least one optical fiber within the heat zonefor processing.
 38. The apparatus of claim 37, wherein the apparatus isconfigured to splice at least two optical fibers in the heat zone. 39.The apparatus of claim 37, wherein apparatus is configured to: taper theat least one optical fiber the heat zone; anneal the at least oneoptical fiber in the heat zone; strip the at least one optical fiber inthe heat zone; or lense the at least one optical fiber in the heat zone.40. The apparatus of claim 37, wherein the positioner is a multi-axispositioner.
 41. The apparatus of claim 32, further comprising: apressure sensor coupled to the controller and arranged to sense a gaspressure within the chamber.
 42. The apparatus of claim 32, wherein thechamber is an airtight chamber.
 43. The apparatus of claim 42, furthercomprising: a flexible seal that enables ingress and egress of the atleast one optical fiber.
 44. The apparatus of claim 42, wherein thechamber comprises: an enclosure; a lid configured to open and close theenclosure; and at least one airtight seal between the lid and theenclosure.
 45. A workpiece processing system, comprising: an airtightchamber configured to maintain a gas in at least a partial vacuum; aplurality of electrodes within the chamber and arranged to generate anarc discharge in a gap between the at least two electrodes to establisha heat zone in the gap; a positioner system configured to position atleast one workpiece within the heat zone for processing; an arcdischarge unit configured to supply a drive current to the at least twoelectrodes at a level sufficient to ionize the arc discharge tosaturation for a chosen gas pressure; a pressure sensor arranged tosense a gas pressure within the chamber; and a controller coupled to thepressure sensor and configured to control a gas pressure within thechamber to responsively control an upper temperature limit within theheat zone. a vacuum generating venturi configured to generate thepartial vacuum within the airtight enclosure and to control the pressureto thereby establish an upper limit of the temperature applied to theworkpiece.
 46. The system of claim 45, wherein the at least twoelectrodes is at least three electrodes.
 47. The system of claim 45,wherein the workpiece holder is at least one multi-axis positioner. 48.The system of claim 45, wherein the workpiece is at least one opticalfiber.
 49. The system of claim 48, wherein the system is configured tosplice at least two optical fibers in the heat zone.
 50. The system ofclaim 48, wherein system is configured to: taper the at least oneoptical fiber the heat zone; anneal the at least one optical fiber inthe heat zone; strip the at least one optical fiber in the heat zone; orlense the at least one optical fiber in the heat zone.